Hollow thermoplastic synthetic resin panels having two parallel sheets and a plurality of ribs integrally connecting together the two sheets are used for forming packages, such as boxes, architectural materials, such as partition members and walls, and the like. The hollow thermoplastic synthetic resin panel for such purposes are produced by extruding a material in the direction of extension of the ribs. Generally, the material is a thermoplastic resin such as a polypropylene rein or a polyethylene resin. The hollow thermoplastic synthetic resin panel has become prevalently used owing to its excellent strength and durability as compared with those of corrugated cardboards,
Since the side edges parallel to the ribs of the conventional hollow panel of this kind, and the end edges of the same hollow panel perpendicular to the ribs are open to the outside, the interior of the spaces of the hollow panel are liable to be contaminated with foreign matters including dust and unwanted bacteria, and the cleaning of the interiors of the hollows is practically impossible. Accordingly, the conventional hollow panel could not have been used for forming boxes for containing food, medical and pharmaceutical products, cosmetics, etc. which must meet severe sanitary standards.
When using hollow panels of this kind as a packaging material, the hollow panels need to be subjected to processes to form grooves and/or recesses in the surface thereof, and to form folding grooves and openings in the hollow panels. Such processes use press working including hot-plate press working. However, since folding grooves formed by press working are shallow and portions of the hollow panels corresponding to the folding grooves are excessively resilient, various troubles arises during and after assembling the hollow panels to form boxes. If an opening is formed in the hollow panel by press working, the interior of the hollows are opened on the edge of the opening and hence the interior of the hollows are contaminated with foreign matters including dust. When a hot plate is used for press working, the surface of the hot plate melts portions on the opposite sides of a pressed part of the opposite sheets of the hollow panel and many pores are formed in the hollow panel.
Hollow panels are joined together or a hollow panel is joined to another part, such as a frame, by methods respectively using staples, rivets, an adhesive tape and an adhesive. These methods have been employed in joining together corrugated cardboards made of paper and, in some cases, these methods are applicable to joining together hollow synthetic resin panels without entailing any problem.
Hollow thermoplastic synthetic resin panels are used for forming a package for containing a heavy article that applies a large load that cannot be born by a corrugated cardboard or fiberboard to the package or a highly air-tight or liquid-tight package. Therefore, a package formed by welding together hollow thermoplastic synthetic resin panels with adhesive tapes or an adhesive is not perfectly reliable when used for such purposes. Stapling and riveting have difficulty in carrying out air-tight or liquid-tight welding.
A method of welding together hollow thermoplastic synthetic resin panels with a hot plate, similarly to the method of forming grooves and/or recesses in hollow thermoplastic synthetic resin panels and forming folding grooves and openings in the hollow thermoplastic synthetic resin panel, has problems in that many holes and impressions are formed in the surface of the hollow thermoplastic synthetic resin panel, and in that two hollow thermoplastic synthetic resin panels, or a hollow thermoplastic synthetic resin panel and a thermoplastic synthetic resin part are not welded firmly together with satisfactory appearance and, in a worst case, the welded portions of the hollow thermoplastic synthetic resin panel are burnt off.
The present invention has been made to solve those problems in the prior art and it is therefore an object of the present invention to provide a hollow thermoplastic synthetic resin panel welding method capable of firmly welding together the opposite sheets of a hollow thermoplastic synthetic resin panel, two hollow thermoplastic synthetic resin panels or a hollow thermoplastic synthetic resin panel and another part with satisfactory appearance.
Another object of the present invention is to provide a thermoplastic synthetic resin panel welding method capable of surely closing the edges or the line of a hollow thermoplastic synthetic resin panel by fusion to seal the interior of the hollow thermoplastic synthetic resin panel panel.
Still another object of the present invention is to provide a thermoplastic synthetic resin panel welding method capable of surely forming grooves, recesses, folding grooves, openings and such in a hollow thermoplastic synthetic resin panel without inducing resilience in portions of the hollow thermoplastic synthetic resin panel corresponding to the grooves, the recesses, the folding grooves, the openings and such.
A further object of the present invention is to provide a hollow thermoplastic synthetic resin panel processed by the foregoing method and a hollow panel structure fabricated by processing hollow thermoplastic synthetic resin panels by the foregoing method.